vorta: strip away output dependency on qt5.qtwayland.dev

`propagatedBuildInputs` is only required in this case to correctly build
the `PYTHONPATH` for the final application. The QT hook doesn't need
`qtwayland` in `propagatedBuildInputs`, `buildInputs` is sufficient for
it to work.

Additionally, this causes a closure-size reduction of ~22.5% because we
get rid of the dependency to the `dev` output of `qtwayland`:

    $ nix path-info -Sh ./result-old
    /nix/store/i8i4p2i3wkjv4y95pp3i421nwg0f1shh-vorta-0.8.12	775.2M
    $ nix path-info -Sh ./result-new
    /nix/store/jcyrkk89my2lh00z7dy8z19xyvlf8yhr-vorta-0.8.12	599.5M

pkgs/applications/backup/vorta/default.nix

@@ -4,6 +4,7 @@
 , wrapQtAppsHook
 , borgbackup
 , qt5
+, stdenv
 }:
 
 python3Packages.buildPythonApplication rec {
@@ -19,6 +20,10 @@ python3Packages.buildPythonApplication rec {
 
   nativeBuildInputs = [ wrapQtAppsHook ];
 
+  buildInputs = lib.optionals stdenv.isLinux [
+    qt5.qtwayland
+  ];
+
   propagatedBuildInputs = with python3Packages; [
     peewee
     pyqt5
@@ -29,8 +34,6 @@ python3Packages.buildPythonApplication rec {
     appdirs
     setuptools
     platformdirs
-  ] ++ lib.optionals stdenv.isLinux [
-    qt5.qtwayland
   ];
 
   postPatch = ''